AUTO-6719: Jenkins/README.md: export FORCE_DEV_BUILD and CODE_SIGNING…

…_FILE as well

* without CODE_SIGNING_FILE docker-compose will fail with:
  ERROR: Cannot create container for service build-simulator: create .: volume name is too short, names should be at least two alphanumeric characters

* and without FORCE_DEV_BUILD:
  /mnt/Jenkins/build-simulator.sh: line 60: FORCE_DEV_BUILD: unbound variable

Jenkins/README.md

@@ -20,6 +20,8 @@ export UNITY_SERIAL=...
 export SIMULATOR_DOCKER_IMAGE=hdrp/simulator
 export PYTHONUNBUFFERED=1
 export UID
+export CODE_SIGNING_FILE=/dev/urandom
+export FORCE_DEV_BUILD=true
 ```
 
 ## Running file/folder check